Field of the Invention
The present invention relates to an image processing apparatus which corrects a lateral chromatic aberration (chromatic aberration of magnification).
Description of the Related Art
Image capturing apparatuses such as digital cameras are used for various purposes. However, various aberrations of an image capturing optical system that is used to form an object image are factors of degrading an image quality of the object image. Among the aberrations, a lateral chromatic aberration is a factor of occurrence of a color shift in the object image. It this respect, conventionally, for example a technology where the lateral chromatic aberration is corrected by image processing based on data of the lateral chromatic aberration of the image capturing optical system previously stored is known.
On the other hand, the number of pixels of an image sensor used in the image capturing apparatus increases year after year, and a size of a unit pixel tends to be reduced. Therefore, even in the lateral chromatic aberration whose amount was not conventionally a substantial problem, it may be a main factor of degrading the image quality. When design data of the image capturing optical system are stored as data of the lateral chromatic aberration, the image quality is degraded by an uncorrected change of the lateral chromatic aberration caused by a manufacturing error of the image capturing optical system. In this specification, the lateral chromatic aberration means a shift of an imaging position for each color (i.e., color shift), and it appears due to a movement of an image in each pixel, differently from a blur caused by an imaging performance. In order to reflect the manufacturing error of the individual image capturing optical system on the data of the lateral chromatic aberration, it is necessary to measure a real aberration amount that changes for each lens parameter at the time of the manufacture, which leads to a decrease in mass productivity and an increase in manufacturing cost. If the change of the lateral chromatic aberration caused by the manufacturing error is not separated as an appropriate component, a correction amount needs to be stored for each pixel. As a result, correction data amount increases or a correction effect is insufficient. technology where the lateral chromatic aberration corresponding to the manufacturing error is corrected based on a rotationally symmetric component with respect to the center of an image and a correction amount calculated as a shift component where an amount and a direction of a color shift is uniform in an entire image.
As the manufacturing error of the image capturing optical system, there are eccentricity from an optical axis or a tilt of a lens element or a lens unit, a position shift parallel to the optical axis direction, a focal length shift caused by a shape or a refractive index of the lens element, and the like. A lateral shift of an image mainly occurs for each color due to the eccentricity or the tilt of the lens element or the lens unit, and a magnification shift of the image occurs for each color due to the position shift parallel to the optical axis direction or the focal length shift of the lens element. However, since Japanese Patent No. 5505135 assumes that the eccentricity from the optical axis and the tilt of the lens element and the lens unit as the manufacturing error, the magnification shift for each color cannot be corrected, and the lateral chromatic aberration changed due to the manufacturing error cannot be corrected satisfactorily.